Compound ingot and method of producing the same



Feb. 19, 1929. 1,702,387

H. A. KUHN I COMPOUND IGNOT AND METHOD OF PRODUCING THE SAME Filed June16, 1927' 3&7

Patented Feb. 19, 1929.

UNITED STATES PATENT OFFICE.

, HARRY A. KUHN, 0F PITTSBURGH, PENNSYLVANIA.

Application filed June 16,

This invention relates to metallurgy or more especially to the castingin still molds of ingots from metals of different composition in suchmanner as to form a finished product characterized by zones of theconstituent metals in substantially homogeneous form with normal,continuity of crystallization throughout the ingot.

Many efforts have been made heretofore to produce an integral compoundingot of the character described. Such an ingot is adapted to many uses,as where a wearin surface of one metal is desired anda body 0another,'or a sheath of rust-resisting metal and an integral core ofcheaper or tougher metal, or a face metal of one strength or characterand a backing metal of another strength or character. Innumerableexamples of the utility of such a composite metal body will be apparentto those skilled in the art. But despite the extraordinary utility andimportance of the subject matter and the attention that has been givento it by engineers, I have not found in the art prior to my inventionany practical solution of the problem nor any means for producing atruly integral compound ingot, i. e., one characterized by zones ofdifferent metals in substantially homogeneous form and by normal bondingand continuity of crystallization throughout.

\Vhere different metals are poured together in liquid or molten phase asheretofore, they mix to form substantially a complete alloy of the twoconstituents by virtue of the characteristic of migration and diffusionof fluids. Even if care be exercised to pour the different metals indifferent zones (as by bottom pouring in a vertical mold) they willmerge to form an ingot hich is characteristically an alloy throughoutits major portion If agitation of themetal in the body of the mold ispermitted the alloy becomes substantially homogeneous. If the metals arebrought into contact in the presence of the atmosphere a line of oxidesis produced which prevents normal crystallization. In centrifugalcasting of two or more metals the crystallization is not normal, thecrystals being deformed by the centrifugal force as they build up in themother liquor.

Where one metal in liquid phase is brought in contact with another insolid phase as by pouring a molten metal on a solid or by welding, asheretofore, an abnormal boundary of crystallization is produced betweenthem.

1927. Serial No. 199,208.

The resulting ingot is somewhat analogous in structure to a block ofconcrete formed by two successive pours where the first batch poured hasbeen permitted to set before the pourin of the second. Each batch willform a bloc having the internal cohesion characteristic of normalcrystallization. But between the two blocks will be a boundarycharacterized only by adhesion. The rocks and crystals of the meetingsurfaces may interlock but there is absent the bonding of the crystalsby the amorphous intercrystalline material which is characteristic ofthe normal setting or freezing of crystalline materials. In pouringmolten metal into contact with solid metal there is a tendency to meltthe surface of the solid metal and to permit interlockingcrystallization between the two on cooling but this tendency is largelyovercome and normal continuity of crystallization is prevented by theinstantaneous cooling effect of the solid metal on the molten whichproduces abnormal crystallization in the latter along the boundary ofcontact. Further, the presence of atmospheric gases during the contactof the metals results in the formation of a line of oxides along withthe abnormal crystalslike a line of dry rubble stone between two massesof concrete-so that on cooling there is little more than adhesion at theboundary which results in cleavage, s litting, etc., in subsequent useor working 0 the metal.

I have discovered that under certain conditions of casting thesedifficulties may be avoided, and an integral compound ingot produced inwhich the major portion of the constituent metals" is found, not in theform of a new alloy, but in zones of metal each having substantially theanalysis of one of the original constituents and in which there is noabnormal boundary of crystallization but apparently normal andcontinuous interlocking crystallization throughout the ingot.

I will now explain my invention in connection with the accompanyingdrawings in which there is illustrated in Fig. 1, in vertical section, aform of mold which may be employed in casting the ingot, in Fig. 2 theupper half thereof, in Fig. 3 a section of such upper half, in Fig. 4the lower half thereof, in Fig. 5 a section of such lower half, in Figs.6, 7 and 8, cross sectional views of an ingot cast in accordance withthe invention, the sections being taken on lines 6-6, 77,- and 8--8respectively of Fig. 9, in Fig. 9 a longitudinal vertical section of aningot cast according to my invention in a mold such as shown in Figs.15, and in Fig. 10 the cross section of another ingot for purposes ofcomparison.

In practicing my invention I prefer to employ a horizontal mold whichmay be of the type shown in Figs. 1 to 5 though any other appropriatetypeof mold may be employed in which agitation due to pouring isminimized in the body of the mold. It will be apparent that in a moldsuch as illustrated much of the time of pouring the metals into the moldthe metal which is to form the sheath is at substantially thetemperature known to founders as on the hot side (which in the case ofchromium or stainless steel may be approximately 2900-3000 'F.),. andthat the metal which is to form the core is at substantially thetemperature known to founders as on the cold side (which in the case ofcarbon :sEt e)el may be approximately 2700 to 2800 Having so preparedthe constituent metals in the form of liquid metal solutions incondition for pouring, the metal which is to form the sheath is firstpoured into the mold. As will be readily understood this liquidsolution, as it is poured in, freezes and solidifies at its boundary ofcontact with the mold,

thus forming a rigid trough or bowl in contact with the walls of themold and containing within it a body of metal solution the generaltemperature of which is on the hot side. Between the body of metal inthe liquid phase, having molecular fluidity, and the trough or bowl ofmetal in the solid phase, having molecular rigidity, there will e noclear line of demarcation, but a zone of viscous, semi-frozen metal inwhich the continuous crystallization, characteristic of freezing, is inprocess and is, in general, proceeding inwardly from the rigid zone tothe fiuid zone with the cooling of the metal.

Meanwhile, and before the pouring of the first metal has been completed,the pouring of the second metal is begun and it is poured in such manneras to form a continuous stream; for example as the stream of the firstmetal is about to disappear out of the teeming pot the second metal maybe poured into this pot so that the stream of steel is continuous. Inaddition, care must be exercised to pour it so as to produce a minimumof a 'tation of the metal in the mold and so that the stream enters themold under the skin of the metal already poured.

. This second metal, being substantially cooler than the body of thefirst metal, appears to flow along the trough or bowl formed in thebottom of the mold by the freezing of the first metal and to displacethe hotter liquid portion of the first metal and carry it rearwardupward along the sides of the mold and finally over the top thereof asthe mold is filled, the first metal continuing to freeze and solidity asit comes in contact with the walls of the mold to form a sheath orcoating for the sides and top comparable to that already formed for thebottom of the ingot. The oxide film which is continuously forming on thetop of the molten metal floats upward progressively to the top of themold and is not to any substantial extent broken up or disseminatedthrough the molten mass. The zone of contact between the two metals isnot exposed to the atmosphere or to the gases in the mold, it is alwaysunder the skin of the molten metal so that no oxide film or the like ispermitted to form between the two to pro duce an abnormal boundary ofcrystallization or interfere in any way with normal continuouscrystallization throughout the ingot,

as it cools. Agitation within the molten mass is avoided as much aspossible to minimize alloying between the respective metals. Thus, thecrystallization, begun in the sheath metal, as aforesaid, and that whichbegins in the body of the somewhat cooler core metal continuesprogressively in accordance with the normal laws of freezing of suchmetals and produces a continuous crystallization be tween the two metalswith normal bonding and integral interlocking of the crystals of the twometals in a zone of alloy between them. After pouring, the mold ispreferably tilted up somewhat at the pouring end so that the pipe willbe restricted to that end. The ingot is then allowed to cool and may beworked in the usual manner.

By this method there is produced an integral, composite ingot having asheath of one substantially homogeneous metal surrounding a core of adifferent substantially homogeneous metal and characterized by theabsence of any structural boundary or line of weakness between them.

It is my understanding of the theory underlying the process describedthat complete alloying of the metals is prevented and such alloying asoccurs is, largely restricted to a zone positioned between the zones ofsubstantially homogeneous metal by reason of the difierence intemperature of the two metals, the contacting thereof under the skin ofthe molten mass and the minimizing of agitation. The colder core metalappears to force aside the hotter sheath metal, thus positioning itselfcentrally of the ingot while at the same time permitting integralsolidification and crystallization of the metals as the ingot cools.This is borne out by an examination of the metals as they appear in thefinished ingot. Such examination makes it clear that while there issometimes a trace of diffusion of metals throughout the ingot there issubstantial alloying only in a limited zone between them; the originalmetals in substantially homogeneous form are separately positioned inthe ingot; there is continuity of normal crystallization throughout theingot; the amorphous fillings between the crystals show no line ofabnormal crystallization; on the contrary they show the integralinterlocking of crystals characteristic of normal freezing. Figs. 6, 7and 8 represent sections cut from an actual ingot cast as I havedescribed. Fig. 6 represents a section cut from the part of the ingotnear the mouth of the mold (see line 66 in Fig. ,9). Fig. 7 represents asection from the middle of the ingot (line 77 of Fig. 9) and Fig. 8 asection from the part of the ingot near the back or closed end of themold (line 88 of Fig. 9). The figures represent such sections after thesame have beenetched with acid to indicate the zones occupied by thechromium and carbon steels. It will be understood by those skilled inthe art that the clear line of demarcation shown by the acid does notindicate an equally clear line of demarcation between the metals. It ismerely a function of the acid used. The line formed by the acidindicates the boundary outside of which the section consists principallyof chromium steel and within which it consists principally of carbonsteel. The line shows the relative positioning of the metals in theingot and demonstrates the existence of a structure such as I havedescribed and which I believe has never been produced prior to myinvention. The positioning of the respective metals in the ingot asdescribed is confirmed by analysis of samples drilled out of thesections. These samples indicate that the major portion of the sheathmetal is homogeneous and of substantially the same analysis as that ofthe metal first poured, that the major portion of the core metal ishomogeneous and of substantially the same analysis as that of the metallast poured, that alloying between the sheath and core metals takesplace in a limited zone between the two, that a trace of the sheathmetal may be sometimes found in the core metal, that/there is normalbonding and interlocking of crystals throughout the ingot. For example,if the metal first poured be 14% chromium steel and the metal lastpoured be ordinary carbon steel, the section outside of the boundaryindicated by the acid line in Figs. 6, 7 and 8 is found by analysis tobe substantially homogeneous 14% chromium steel, the core substantiallyhomogeneous carbon steel with an alloy of the two extending in a limitedzone between the core and sheath metal. Analysis of samples taken fromthe oints marked A in Fig. 6 shows no appreciafile evidence of thepresence of migrating or alloying of chrome. Analysis of samples takenfrom the points marked B in Fig. 8 shows 1% to 1 of chrome present.Analysis of samples taken from the points marked C in Fig. 8 shows 2% to3% of chrome present. This slight evidence of migration of the chrome inthe far end of the ingot is not such as would result from normalalloying of the two metals, it is notably less than has occurred inprior practice.

Comparison of Figs. 6. 7 and 8 indicates that in the ingot from whichthey were taken the sheath metal was forced by the colder core. metaltoward the rear or closed end of the mold as well as upward around thesides and top of the mold so that the sheath is much thicker at thebottom end of the mold than at the open or inletend. Indeed, in Fig. 6,the sheath appears not to have been continuous but to consist of a zoneat the bottom and lower sides and a separate zone across the toNon-uniformity of sheath depth may be of advantage where articles ofdifferent character are to be made from the ingot. Thus the ingot may becut in a plurality of parts, that from the portion of the ingot nearestthe open end being used where the minimum ratio of sheath to core metalis desired and that from the portion of the ingot nearest the bottom orclosed end of the mold being used where the greatest ratio of sheath tocore metal is needed. 1

In Fig. 10 I show a typical cross section of an ingot made by pouringinto a similar mold and in similar manner first a solution of copper and20% nickel'-the same hing poured at a temperature of about 2300 F-andsecond molten carbon steel at a temperature of about 27OU-- 2800 F. Itwill be observed that the metal first poured has remained in the bottomof the mold. If instead of the solution stated (80% copper, 20% nickel)Monel metal had been used 'at a temperature of about 2900 F. the resultwould be substantially the same as shown in Figs. 6, 7 and 8. SinceMonel metal and the solution stated have substantially the same specificgravity, both being heavier when cold than carbon steel, I attribute theformation of the sheathed ingot shown in Figs. 6, 7 and 8 to thedifference in temperature of the metals employedi. e., the temperatureof the metal first poured being higher than that of the metal nextpoured; I attribute the continuity of crystallization to the conditionspermitting the metals to contact in fluid phase without atmosphericcontact or sufiicient temperature difference between them to produceabnormal volatilization of contained compounds; I attribute therestriction of molecular migration within a limited zone, i. e.,prevention of ordinary alloying throughout the ingot, to the visillcosity of the respective metals due to their temperatures. The resultingcomposite integral ingot therefore appears to be the result of functionsof temperature of the metals rather than of their specific gravities.

While I have described my invention by reference to a specificembodiment thereof, it

will be understood that the same is illustrative only and that l do notintend to limit the definition of my invention except as defined by theannexed claims. it will be understood that in describing as metals thematerials used in casting ingots according to my invention T intend toinclude appropriate alloys as well.

at l claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A compound ingot comprising zones of different metals insubstantially homogeneous form with normal continuity ofcrystallizationthroughout the ingot.

. 2. A compound in ot comprising difierent metals in substantiallyhomogeneous form in difi'erent zones, a zone of alloy between them i andnormal continuity of crystallization throughout the ingot. i

3. A compound ingot comprising a substantially homogeneous core, asubstantially homogeneous sheath of different metal with normal andcontinuous interlocking crystallization throughout the ingot.

4. A compound ingot comprising a substantially homogeneous core, asubstantially homogeneous sheath of heavier metal than the core withnormal and continuous interlocking crystallization throughout the ingot.

5. A compound ingot comprising a substantially homogeneous core, asubstantially homogeneous sheath of heavier metal than the core, arestricted zone of alloy between the sheath and core, with continuouscrystallization and bonding of crystals throughout the ingotcharacteristic of normal freezing of such metals. p

6. A compound ingot comprising a sheath of one metallic alloy, a core ofanother metallic alloy containing only a minor percentage of moleculesof the first alloy, a restricted zone of alloy of the two alloys betweenthem and continuous crystallization and bonding of crystals throughoutthe ingot characteristic of normal freezing of such alloys.v

7 A compound ingot comprising metals of different composition separatelypositioned in the ingot and integrally bound together by a zone ofalloy, the structure and bondin of crystals between said metals and saida loy being continuous and free from abnormal boundaries. i R

8. The method of casting an ingot which" consists in pouring a metalinto a mold and then pouring a second metal at a lower temperature underthe skin of the first metal without substantial agitation.

9. The method of casting an ingot which moaaev consists in pouring ametal into a mold thereby producing zones of the metal characterized bymolecular rigidity and molecular fluidity and then introducing betweenthe two zones a molten metal at a temperature intermediate that of thetwo zones.

10. The method of casting an ingot which consists in pouring a metalinto a mold thereby producing zones of the metal characterized by asubstantial temperature difference and the metal in one of said zonesbeing fluid and then introducing between the two zones a molten metal ata temperature intermediate that of the two zones.

11. The method of casting an ingot which consists in pouring a metalinto a mold there by producing a zone of the metal more viscous than anoverlying zone thereof and then'introducing into such viscous zone,substantially without agitation and without exposure to oxidizing gases,a molten metal at a temperature below that of the overlying zone.

12. The method of casting an ingot which consists in pouring a metalinto a mold thereby producing a zone of the metal more viscous than anoverlying zone thereof and then introducing under the skin of the firstmetal and without substantial agitation a molten metal at a temperaturebelow that of the said overlying zone.

13. The method of casting an ingotwhich consists in freezing a portionof molten metal partially surrounding another portlon of the same metalin liquid phase, introducing under the slzin of the first metal andwithout substantially agitating it, a difl erent metal in liquid phaseand at a temperature less than that of the fluid portion of the firstmetal,

' ermitting the second metal to replace the uid portion of the firstmetal within the frozen portion thereof and freezing said displacedportion about the top and sides of said second metal to form an integralsheath therefor on cooling of the ingot.

14. The method of casting an ingot which consists inpouring into a moldsuccessively and in continuous stream two molten metals the first ofwhich is heated to a temperature higher than that of the second andpermitting the stream of the second metal to enter into the body of thefirst metal and to spread therein without substantially agitating thefirst metal.

15. The process of producing a compound ingotwhich comprises heating twometals to different temperatures and then pouring the cooler metal intothe hotter metal 1n the absence of oxidizing gases and withoutsubstantially agitating the hotter metal.

16 The process of producing a compound ingot which comprises'positioninga metal in a mold, permitting rapid cooling of the metal in contact withthe floor of the mold, pouring a second metal under the skin of thefluid portion of the first metal and directing the stream of secondmetal laterall across the cooling portion oi the first meta 17. Theprocess of producing a compound ingot which includes positioning amolten metal in a mold in zones characterized by molecular viscosity andmolecular fluidity, pouring a second metal under the skin of the firstwhile at a temperature below that of the first metal in the fluid zoneand directing the stream of the second metal into the viscous zone ofthe first metal.

18. The process of bonding together two dillerent metals in normal andcontinuous crystalline structure which consists in forming a pool of onemetal and then gently flowing the second metal under the skin of thefirst metal to produce extending contact between the two metals, underthe surface of the first, the pouring temperature of the second metalbeing lower than that of the first.

19. The process of forming a com ound integral ingot of different metalswit out substantial alloying thereof which consists in pouring the firstmetal into a mold to form zones characterized by molecular viscosity andmolecular fluidity and then gently flowing the second metal, while at atem erature below that of the fluid zone of the rst, into the Viscouszone of the first, thereby displacing the first metal from the center ofthe mold and substantially preventing alloying of the two metals exceptin a restricted zone between them.

In testimony whereof, I. have signed my name to this specification.

HARRY A. KUHN.

